pyroxene

Any of a group of dark, dense, rock-forming silicate
minerals rich in calcium, iron, and magnesium and commonly found in basalt.
Pyroxenes are monoclinic or orthorhombic, have a chain structure, with prismatic
cleavage close to 90°, and are related
to the amphiboles. The group includes
augite, hypersthene,
and diopside, with composition varying as a mixture of FeSiO3,
MgSiO3, and CaSiO3. Pyroxenite is
an igneous rock composed largely of pyroxene.
Jadeite and spodumene are commercially important.